This invention relates to a sterilization apparatus suitable for the sterilizing treatment of liquids or pastes of food and medicines containing solid particles, and particularly to a sterilizing apparatus capable of collecting the products alone under a stable pressure to the inside of the apparatus and continuously discharging hot water during sterilization of the apparatus, water during operation with water, and a mixture of water and the products during change-over operation while maintaining the sterility of the product passages.
It is widely known that putrefaction occurring during storage of food and medicines is generally caused by microorganisms. In order to eliminate putrefaction of food and medicines, techniques for increasing the preservability of food and medicines by processing them with a bacteriological stable condition have been developed. One of the typical techniques is sterilization by heating of packed products as seen in canned and retort foods. In this technique, however, the inside of the containers has to be heated for a long period of time so as to kill the bacteria. A great problem of this technique, particularly in connection with food and medicines, is that heating for a long period of time impairs taste, efficacy and nutritional value and breaks down tissue.
It is preferred to carry out heating for a short time at a high temperature in sterilization of food and medicines. Recently, a method and an apparatus for sterilizing products at a high temperature in a short time before placing them into a container has attracted much attention along with aseptic packaging for packing of sterilized products in a contained under aseptic conditions.
Sterilization of food and medicines is usually carried out at a high temperature over 100.degree. C., and boiling of the products occurs in the sterilizer at atmospheric pressure. Therefore, sterilization by heating must be carried out in the sterilizer under a pressure (termed as the backpressure hereinafter) so as to prevent boiling. In this respect, the conventional method and apparatus involved various problems.
More specifically, the conventional apparatus is provided with a feed pump for feeding the products into the sterilizer and a pump for sending the sterilized products to the next process, on the inlet and outlet ends of the sterilizer. A backpressure is applied to the sterilizer by control of the discharge rate of the pumps.
However, pulsation of or leakage from the pumps brings about fluctuations in the flow rate of the product passing through the sterilizer. This causes a change in backpressure applied to the sterilizer. Thus, the conventional apparatus has drawbacks in its pump functions. In the conventional apparatus, therefore, it was difficult to supply a stable backpressure to the sterilizer, and to sterilize the products under stable conditions.
In addition, it is difficult in the conventional apparatus to control accurately the backpressure to a desired value.
Furthermore, if the sterilization conditions are established so as to make the product aseptic, a very high temperature and a high pressure must be supplied to the rear pump. It is, therefore, difficult to sterilize the product under constant conditions from the viewpoint of the above pump functions. This is a fatal problem in an aseptic packaging apparatus. Also, if a rear pump is used which can endure a high temperature and high pressure, while maintaining aseptic conditions, the pump must be made of special materials and with a special design. In addition, it is difficult to obtain a stable flow rate in the low and high temperature zones in the apparatus.
If the product contains solid particles, most of the solid particles are broken up according to the above method, since the product passes twice through the pumps.
If the rear pump is replaced by a pressure relief valve or a homogenizer in the above method, it is possible to apply a fairly constant backpressure to inside apparatus. However, if the product contains solid particles or is highly viscous, accumulation of particles and blockage occurs at the pressure relief valve or the homogenizer, and causes troubles such as destruction of the apparatus due to an abnormal increase in pressure inside the apparatus. Therefore, the homogenizer or the pressure relief valve cannot be used in treating such products.
A sterilization apparatus suitable for sterilizing materials containing solid particles was described in a generally circulated West German magazine (Die Molkereizeitung Welt der Milch, 35. Jahrgang, 1981/41). This apparatus, which solves the above problems, is equipped with a feed pump in front of the sterilizer and a backpressure tank behind the sterilizer. In the sterilization apparatus, the backpressure tank is capable of controlling the air pressure, and a backpressure is supplied to the sterilizer by use of the air pressure in the backpressure tank. Therefore, even if the product contains solid particles, it is possible to treat it under constant high temperature conditions and stable application of a backpressure to the steilizer. Also, no clogging of solid particles occurs in the apparatus.
The sterilizing apparatus described in the magazine shows an excellent effect in sterilizing products containing solid particles as described above. However, the magazine refers only to the basic structure of an apparatus comprising a feed pump, a sterilizer and a backpressure tank, and clarifies the principle of applying a backpressure to the sterilizer by the air pressure.
In actual operation of the sterilizing apparatus, sterilization of the apparatus to secure the sterility of the whole apparatus before starting operation, operation with water, and change-over operation from water to products are required before operation with the product. Therefore, the sterilization apparatus must be equipped with mechanisms corresponding to each such step.
A conventional apparatus for sterilizing milk, or other products comprises, for example, a sterilizer, pumps before and behind the sterilizer, a device for recovering the milk or product provided behind the rear pump, and a device for discharging treated materials other than the milk or product. In the above apparatus, a backpressure is supplied to the sterilizer by means of the pumps, and all materials including hot water used for sterilizing the apparatus, water, a mixture of water and milk or the product, and the sterilized milk or product pass through the pump behind the sterilizer, and are then discharged or recovered.
In the apparatus for sterilizing milk, it is possible to carry out the operation from sterilization of apparatus to operation with the product by passing the product through the pump behind the sterilizer without installation of independent piping, etc. This is because the physical properties of hot water used for sterilization of the apparatus are similar to those of milk, and milk contains no solid particles.
However, if products containing solid particles are treated, it is impossible to satisfactorily carry out all processes from sterlization of the apparatus to recovery of the products in such an apparatus in which the rear pump in the above apparatus is replaced by a backpressure tank, i.e., an apparatus according to prior art as described above.
If materials containing solid particles are treated in the conventional apparatus, all of the hot water used for sterilization of the apparatus, the water used during operation with water, the mixture of water and the product used during change-over operation and the product are sent into the backpressure tank. Therefore, it is difficult to collect the products alone in a continuous operation from sterilization of the apparatus to operation with products under a backpressure.
Thus, in order to satisfactorily sterilize products containing solid substances the sterilization apparatus should have a structure capable of continuously discharging the treated materials other than the product and collecting the products alone under a stable backpressure to the inside of the apparatus while maintaining the sterile condition of the product passages.